There is known a separation technique for separating dielectric particles such as bacteria and cells by using dielectrophoresis, and in order to separate this type of dielectric particles, there is known an analysis technique for analyzing a crossover frequency at which a dielectrophoretic force on the dielectric particles switches from a repulsive force to an attractive force or from the attractive force to the repulsive force.
Patent Document 1 discloses a characteristic analysis method of optimizing an AC voltage frequency to be applied in performing characteristic analysis on particulate matter by using dielectrophoresis. This characteristic analysis method includes the steps of: selecting at least one particulate matter in a fluid; positioning the selected particulate matter in the vicinity of a pair of electrodes; generating a spatially inhomogeneous electric field between the pair of electrodes by using a programmed voltage signal including a frequency-modulated AC voltage; detecting the movement of the particulate matter while applying the programmed voltage signal to create time-series data on the movement of the particulate matter; and analyzing the characteristics of the particulate matter based on the time-series data. The time series data is moving image data obtained by capturing an image of movement of the particulate matter, and the moving image data includes data of imaging time. The step of analyzing the characteristics of the particulate matter includes the steps of: displaying data of the imaging time together with the moving image data on a display; obtaining the time when the selected particulate matter stays in the vicinity of the tip of one of the pair of electrodes based on the moving image data displayed on the display, and calculating a boundary frequency at which the dielectrophoretic force on the selected particulate matter switches from the attractive force to the repulsive force based on the obtained time.